In the wireless communication technology, when a base station side (such as evolved Node B, that is, eNB) transmits data with a plurality of antennas, spatial multiplexing may be used to increase the data transfer rate, that is, the transmitting end uses the same time-frequency resource to transmit different data at different antenna positions, and the receiving end (such as the user equipment (UE)) also uses a plurality of antennas to receive the data. In the case of a single user, the resources of all antennas are assigned to the same user, and this user alone occupies the physical resources allocated by the base station within one transmission interval, this transmission method is called a single user multiple-input multiple-output (referred to as SU-MIMO); in the case of multiple users, the spatial resources of different antennas are allocated to different users, one user and at least one another user share the physical resources allocated by the base side within one transmission interval, the sharing method can be space division multiple access or space division multiplexing, and this transmission method is called Multiple User Multiple-Input Multiple-Out-put (referred to as MU-MIMO), in which the physical resources allocated by the base station refer to the time-frequency resources. If the transmission system needs to simultaneously support the SU-MIMO and MU-MIMO, the eNB needs to provide the data in these two modes for the UE. Both in the SU-MIMO mode and the MU-MIMO mode, the UE needs to know the rank used by the eNB for the transmission of the MIMO data. In the SU-MIMO mode, the resources of all antennas are allocated to the same user, the number of layers used to transmit the MIMO data is equal to the rank used by the eNB for transmitting the MIMO data; in the MU-MIMO mode, the number of layers corresponding to one user transmission is less than the total number of layers for the eNB transmitting the MIMO data, if it needs to switch between the SU-MIMO mode and the MU-MIMO mode, the eNB needs to notify the UE of different control data in different transmission modes.
In the Long Term Evolution (LTE) system, the control signaling that needs to be transmitted in the uplink includes Acknowledgement/Negative Acknowledgement message (ACK/NACK), and three forms for reflecting the downlink physical channel state information (CSI): Channels quality indication (CQI), Pre-coding Matrix Indicator (PMI), and Rank Indicator (RI).
The CQI is an indicator used to measure the grades of the downlink channel quality. The CQI is represented with integer values from 0 to 15 in the 36-213 protocol, an the values respectively represent different CQI grades, and different CQIs correspond to their own MCS, see Table 1. The CQI grade selection should follow the following guidelines:
the selected CQI grade is such that the block error rate of the PDSCH transmission block corresponding to said CQI in the corresponding MCS does not exceed 0.1.
Based on a non-limiting detection interval in the frequency domain and the time domain, the UE acquires the highest CQI value, corresponding to each maximum CQI value reported in the uplink sub-frame n. The range of the CQI serial numbers is 1-15 and satisfies the following condition, and if the CQI serial number 1 does not satisfy the condition, the CQI serial number is 0: the error rate of a single PDSCH transmission block does not exceed 0.1 when being received, and the PDSCH transmission block comprises the joint information: the modulation method and transmission block size, which corresponds to one CQI serial number and the occupied a set of downlink physical resource blocks, that is, the CQI reference resource. Wherein, said highest CQI value refers to the maximum CQI value when ensuring the BLER not greater than 0.1, and this helps to control the resource allocation. Generally, smaller the CQI value is, more resources are occupied, and better the BLER performance is.
The joint information of the transmission block size and the modulation method corresponds to a CQI serial number, if: according to the transmission block size, this joint information transmitted by the PDSCH in the CQI reference resource can be notified with signaling, in addition: the modulation scheme is characterized with the CQI serial number and is used in the joint information including the transmission block size and the modulation scheme in the reference resource, and the effective channel code rate produced by it is the effective channel code rate that is possibly closest to the one that can be characterized by the CQI serial number. When there is more than one joint information and they all can produce effective channel code rates that are similarly close to the one characterized by the CQI serial number, the joint information with the smallest transmission block size is used.
Each CQI serial number corresponds to one modulation scheme and one transmission block size, the correspondence between the transmission block size and the NPRB is shown in Table 1. The code rate can be calculated based on the transmission block size and the NPRB size.
TABLE 14-bit CQI TableCQI indexmodulationcode rate × 1024efficiency0out of range1QPSK780.15232QPSK1200.23443QPSK1930.37704QPSK3080.60165QPSK4490.87706QPSK6021.1758716QAM3781.4766816QAM4901.9141916QAM6162.40631064QAM4662.73051164QAM5673.32231264QAM6663.90231364QAM7724.52341464QAM8735.11521564QAM9485.5547
There are a lot of definitions on CQI in the LTE, and depending on different principles, the CQI can be divided:
according to the measurement bandwidth, the CQI can be divided into wideband CQI and subband CQI;
said wideband CQI refers to channel state indications of all the subbands, and what is obtained is the CQI information of the sub band set S;
the subband CQI is the CQI information for each sub-band. Depending on different system bandwidths, the LTE divides the RB corresponding to the effective bandwidth into a plurality of RB groups, and each RB group is called a subband.
The subband CQI can further be divided into full sub-band CQI and Best M CQI: and the full subband CQI reports the CQI information of all subbands; the Best M CQI is M subbands selected from the subband set S, and the CQI information of said M subbands are reported, and the location information of these M subbands are reported simultaneously.
According to the number of code streams, the CQI can be divided into single stream CQI and dual stream CQI;
single stream CQI: used in the single-antenna transmission port 0, port 5, transmit diversity, MU-MIMO, the closed-loop spatial multiplexing of RI=1, and at this time, the UE reports the CQI information of the single code stream;
dual stream CQI: used in closed-loop spatial multiplexing mode. For the open-loop spatial multiplexing mode, since the channel state information is unknown, and the dual-stream characteristic is equalized in the precoding, under the open-loop spatial multiplexing, the CQIs of the two code streams are equal.
The CQI can be divided into absolute value CQI and differential CQI according to the CQI representation method;
the absolute value CQI is the CQI index represented with 4 bit in Table 1;
differential CQI is the CQI index represented with 2 bit or 3 bit; the differential CQI is further divided into differential CQI of the second code stream with respect to the first code stream, and differential CQI of the subband CQI with respect to the subband CQI.
According to the CQI reporting method, the CQI is divided into wideband CQI, UE selected (subband CQI), and High layer configured (subband CQI);
wideband CQI refers to the CQI information of the subband set S;
UE selected (subband CQI) is the Best M CQI, and feeds back the CQI information of the selected M subbands, and reports the position of the M subbands at the same time;
High layer configured (subband CQI) is the whole subband CQI, and for each sub-band, feeds back one CQI information.
The High layer configured and the UE selected are subband CQI feedback method, and in the aperiodic feedback mode, the subband sizes defined in these two feedback methods are inconsistent; in the UE selected mode, M size is also defined.
In the LTE system, the ACK/NACK response message is transmitted in the physical uplink control channel (PUCCH) in the format of 1/1a/1b (PUCCH format 1/1a1/b), when the terminal (UE: User Equipment) needs to transmit the uplink data, it transmits the data in the physical uplink shared channel (PUSCH), and the CQI/PMI and RI feedback may be a periodic feedback, or an aperiodic feedback, and the specific feedback is shown in Table 2:
TABLE 2uplink physical channels corresponding to theperiodic feedback and aperiodic feedbackPeriodic CQIAperiodic CQIScheduling Modereport channelreport channelFrequency non-selectivePUCCHFrequency selectivePUCCHPUSCH
Wherein, for the periodically fed-back CQI/PMI and RI, if the UE does not need to send the uplink data, the periodically fed-back CQI/PMI and RI are transmitted on the PUCCH in the format of 2/2a/2b (PUCCH format2/2a/2b), if the UE needs to transmit the uplink data, the CQI/PMI and RI are transmitted on the PUSCH; for the aperiodically fed-back CQI/PMI and RI, they are transmitted only on the PUSCH.
The Long-Term Evolution (abbreviated as LTE) Release 8 standards defined the following three downlink physical control channels: Physical Control Format Indicator Channel (referred to as PCFICH), Physical Hybrid Automatic Retransmission Request Indicator Channel (referred to as PHICH) and Physical Downlink Control Channel (referred to as PDCCH). Wherein the PDCCH is used to carry the downlink control information (referred to as DCI), comprising: downlink and uplink scheduling information, and uplink power control information. The DCI format is divided into the following types: DCI format 0, DCI format 1, DCI format 1A, DCI format 1B, DCI format 1C, DCI format 1D, DCI format 2, DCI format 2A, DCI format 3 and DCI format 3A, and so on; wherein the transmission mode 5 supporting the MU-MIMO uses the downlink control information of the DCI format 1D, the Downlink power offset field δpower-offset in the DCI format 1D is used to indicate the information that a user's power is halved (i.e. −10 log 10(2)) in the MU-MIMO mode, since the MU-MIMO transmission mode 5 only supports the MU-MIMO transmission of two users, with this downlink power field, the MU-MIMO transmission mode 5 may support the dynamic switching of the SU-MIMO mode and the MU-MIMO mode, but regardless whether it is in the SU-MIMO mode or the MU-MIMO mode, the DCI format only supports one stream transmission for one UE, although the LTE Release 8 supports the single-user transmission of up to two streams in the transmission mode 4, since the switching between the transmission modes can only be semi-static, the dynamic switching between the single user multi-stream transmission and multi-user transmission cannot be achieved in the LTE release 8.
In the LTE release 9, in order to enhance the downlink multi-antenna transmission, the double beamforming transmission mode is introduced, and is defined as the transmission mode 8, while the downlink control information adds the DCI format 2B to support such a transmission mode, an identity bit of scrambling identity (referred to as SCID) in the DCI format 2B is used to support two different scrambling sequences, and the eNB can allocate these two scrambling code sequences to different users, and multiplexes multiple users in the same resource. Furthermore, when there is only one transmission block enabled, new data indicator (NDI) bit corresponding to the disabled transmission block is also used to indicate the antenna port in single-layer transmission.
Furthermore, in the LTE release 10, in order to further enhance the downlink multi-antenna transmission, a new closed-loop spatial multiplexing transmission mode is added and defined as the transmission mode 9, and the downlink control information adds the DCI format 2C to support this transmission mode, and this transmission mode can support both the single user SU-MIMO and also the multi-user MU-MIMO, and it can support the dynamic switching between these two, moreover this transmission mode further supports the 8-antenna transmission. This new transmission mode has decided to use the UE Specific Reference Signal (referred to as the URS) as the pilot for demodulation, and the UE needs to obtain the pilot location to estimate the channel and interference on the pilot.
In the R10 version, the UE is semi-statically configured through the high layer signaling to receive the PDSCH data transmission according to the PDCCH indication of a UE-Specific searching space based on one of the following transmission modes:
Transmission mode 1: single-antenna port; port 0
Transmission mode 2: Transmit diversity
Transmission mode 3: Open-loop spatial multiplexing
Transmission mode 4: Closed-loop spatial multiplexing
Transmission mode 5: Multi-user MIMO
Transmission mode 6: Closed-loop Rank=1 precoding
Transmission mode 7: Single-antenna port; port 5
Transmission mode 8: dual-stream transmission, namely double beamforming
Transmission mode 9: up to 8 layer transmission
In the R10 version, the transmission mode 9 and Channel-State Information-Reference Symbol (CSI-RS) are newly added, and the transmission mode 9 performs the channel measurement based on the CSI-RS or the CRS (Cell-specific reference signals) to calculate and obtain the CQI. Other transmission modes perform channel measurement based on the CRS, so as to calculate the CQI. In the R10 version, it also correspondingly adds some CSI-RS parameters to characterize its properties. Compared to the CRS in the R8, some parameters are similar, and some other parameters are new. For example, the number of CSI-RS ports has a similar number of CRS ports in the R8, while the CSI RS sub-frame configuration periodic parameter is new. The following parameters are cell specific and configured by the higher layer signaling, and are used to define the CSI-RS, comprising: the number of CSI-RS ports, CSI RS configuration, CSI RS subframe configuration parameter ICSI-RS, subframe configuration cycle TCSI-RS, sub-frame offset and an assumption of controlling the reference PDSCH transmission power used by the UE for the CSI feedback.
In the frequency domain, the CSI reference resource is defined by a set of downlink physical resource blocks, and the downlink physical resource blocks correspond to the frequency band corresponding to the source CQI value; in the time domain, the CSI reference resource is defined with a downlink subframe; on the transmission layer domain, the CSI reference resource is defined with any RI and PMI, wherein the CQI is based on the PMI/RI.